The purpose of this clinical trial is to test the hypothesis that the mitral valve apparatus (leaflet, chordae tendineae and papillary muscles), if left intact at the time of valve replacement, will prevent the nearly uniform postreperfusion left ventricular dilation and low cardiac output associated with surgical treatment of mitral insufficiency of long duration. The specific aims are: (1) measure LV hemodynamics and dimensions with ultrasound prior to and after cardiopulmonary bypass in the OR; (2) replace the mitral valve in patients with pure mitral regurgitation with and without resection of the entire mitral valve apparatus; (3) determine immediate postoperative hemodynamic characteristics of each group; (4) analyze 6 month and 3 year results in terms of exercise capacity, LV dimensions, and hemodynamic criteria. The rationale of this investigation is that if the immediate postbypass course of patients receiving mitral valve replacement for long-standing mitral insufficiency can be altered by the mechanism of preventing left ventricular dilation by maintaining the innate physical structures of the left heart, operative mortality and support measures may be reduced and long-term benefits may accrue. The results in five patients have been excellent. Two patients have required postoperative support. There have been no perio-operative deaths associated with the procedure.